Answer:
Consider the ground level as 0 (zero)
Jin is 3 floors above ground level in a hotel.
Hence Jin is in third floor from the ground level (0,1,2 and 3rd floor)
Leila is on a parking level of the hotel that is 4 floors below ground level.
Since the parking is below, it is named as -4 th floor (0, -1, -2, -3 and -4th floor)
They are part by 7 floors, 3 - (-4) = 7